In the development of radio communication systems, such as mobile communication systems (like for example GSM (Global System for Mobile Communication), GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunication System) or the like), efforts are made for an evolution of the radio access part thereof. In this regard, the evolution of radio access networks (like for example the GSM EDGE radio access network (GERAN) and the Universal Terrestrial Radio Access Network (UTRAN) or the like) is currently addressed. Such improved radio access networks are sometimes denoted as evolved radio access networks (like for example the Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) or as being part of a long-term evolution (LTE) or LTE-Advanced. Although such denominations primarily stem from 3GPP (Third Generation Partnership Project) terminology, the usage thereof hereinafter does not limit the respective description to 3GPP technology, but generally refers to any kind of radio access evolution irrespective of the underlying system architecture. Another example for an applicable broadband access system may for example be IEEE 802.16 also known as WiMAX (Worldwide Interoperability for Microwave Access).
In the following, for the sake of intelligibility, LTE (Long-Term Evolution according to 3GPP terminology) or LTE-Advanced is taken as a non-limiting example for a broadband radio access network being applicable in the context of the present invention and its embodiments. However, it is to be noted that any kind of radio access network may likewise be applicable, as long as it exhibits comparable features and characteristics as described hereinafter.
In the context of LTE and LTE-Advanced (i.e. in the context of release 8 and release 10 specifications) and even beyond in later releases, mechanisms for admission control are specified e.g. for handover, bearer setup and bearer modification purposes.
FIG. 1 shows a signaling diagram of an admission control procedure for handover preparation in accordance with LTE and LTE-Advanced.
As shown in FIG. 1, in handover preparation for a user equipment UE, a source base station eNB takes, based on measurement reports it gets from the UE, a handover decision to handover the UE towards a target base station eNB. Then, the source eNB, i.e. the base station which presently serves the UE, sends a handover (HO) request towards the target eNB, i.e. the base station which is to serve the UE after the handover. The target eNB performs admission control for the UE, and acknowledges the handover request towards the source eNB. Then, the source eNB may, after uplink (UL) resources having already been allocated, allocate downlink (DL) resources, and perform radio resource control (RRC) including mobility control information towards the UE.
In the development of cellular systems in general, and access networks in particular, relaying has been proposed as one concept. In relaying, a user equipment or terminal (UE) is not directly connected with an access node such as a radio base station (e.g. denoted as eNodeB or eNB) of a radio access network (RAN), but via a relay node (RN). Relaying by way of RNs has been proposed as a concept for coverage extension in cellular systems. Apart from this main goal of coverage extension, introducing relay concepts can also help in providing high-bit-rate coverage in high shadowing environments, reducing the average radio-transmission power at the a user equipment (thereby leading to long battery life), enhancing cell capacity and effective throughput, (e.g. increasing cell-edge capacity and balancing cell load), and enhancing overall performance and deployment cost of radio access networks.
FIG. 2 shows a schematic diagram of a typical deployment scenario of a relay-enhanced access network, such as e.g. a Long Term Evolution (LTE) RAN with radio-relayed extensions. As shown in FIG. 1, UEs at disadvantaged positions such as a cell edge and/or high shadowing areas are connected to a so-called donor base station (DeNB) via a respective RN. The link between DeNB and RN may be referred to as backhaul link, relay link or Un link, and the link between RN and UE may be referred to as access link or Uu link.
A UE Evolved Packet System (EPS) bearer may be considered as a virtual connection between a core network (CN) and the UE, which is characterized by different quality of service (QoS) parameters, and as such the traffic belonging to this bearer will be treated according to these parameters on the different nodes between the gateways and the UE. On the other hand, RN bearers, also referred to as Un bearers, are defined between the RN and DeNB. The mapping of UE EPS bearers and RN bearers can be done either one-to-one (where there is one Un bearer for each UE EPS bearer), or many-to-one (where several UE EPS bearers are mapped into one Un bearer). The many-to-one mapping can be based on mapping criteria such as the QoS requirements or can be done on a per UE basis (i.e. one Un bearer for all bearers of a given UE, regardless of QoS).
In the context of LTE and LTE-Advanced, a Layer 3 (L3) RN, also referred to as Type I RN, is currently taken as a baseline case for the study on relay extensions. Currently, four options for candidate relay architectures are conceivable, the details thereof being out of scope of the present invention. The four candidate relay architectures may be grouped into two categories.
In a relay architecture of a first category, the DeNB is not aware of the individual UE EPS bearers. That is, the relayed UEs are hidden from the DeNB, and the DeNB is aware of only the RNs with which the relayed UEs are connected. Thus, in such a relay architecture only many-to-one mapping is supported, and specifically QoS based mapping (assuming the QoS mapping is done in a node before the DeNB through a marking of the IP headers Type of Service (TOS) field, for example, in accordance with the a QoS parameter such as Quality of Service class identifier (QCI)).
In a relay architecture of a second category, the DeNB is aware of the individual UE EPS bearers of all of the relayed UEs. That is, the DeNB is aware of the relayed UEs as well as of the RNs with which the relayed UEs are connected. Thus, in such relay architecture, it is possible to support both many-to-one (including per UE based mapping) and one-to-one mapping, and the mapping can be done at the DeNB itself, as the UE EPS bearer's information is visible at the DeNB. Even if many-to-one mapping is used, a more appropriate mapping can be employed in the second category architecture as compared with the first category because all the QoS parameters (in addition to the QCI) can be used in the mapping process. In this case it is possible for example to map bearers of different UEs with similar QoS requirements to a Un bearer that fits these QoS requirements.
The split of resources between the DeNB-RN link and the RN-UE link may be done dynamically or semi-dynamically depending on the number of UEs connected to the DeNB and to the RNs. In the following, centralized resource partitioning is assumed, where the DeNB assigns the resources that each RN connected to it can use to serve its connected UEs. The user scheduling is done at the RNs assuming only the resources assigned by the DeNB are available. Yet, it is noted that distributed resource partitioning may be equally used as well.
In the context of LTE and LTE-Advanced with relaying, no mechanisms for admission control, e.g. for handover, bearer setup and bearer modification purposes, are specified so far. The mechanisms for admission control specified for release 8 as outlined above are not properly and efficiently applicable in such a relay-based deployment scenario.
In particular, the use of admission control mechanisms of release 8 would, in such a relay-based deployment scenario, incur additional delays and additional signaling overhead. Also, additional delay and additional signaling overhead would be incurred, if admission control for certain resources fails. These drawbacks are specifically adverse due to the fact that the frequency of handovers (and, thus, the frequency of required bearer admission control procedures) is increased with the introduction of relay nodes, as well as the fact that the multi-hop nature of the connection between user equipment and base station increases delay and signaling overhead anyway.
Accordingly, the requirements for handovers and other bearer setup or modification procedures according to LTE or LTE-Advanced may not be met in a relay-based deployment scenario when applying conventional admission control mechanisms.
Accordingly, a feasible solution does not exist for facilitating efficient admission control in relay-enhanced access networks.